Research reportSpecificity of the failure to inhibit responses in overweight children
Highlights
• Inhibition of responses towards food and toy pictures is measured in children. • Overweight children inhibited responses to food less effectively than lean children. • No difference between groups was found in the toy condition. • Poor inhibitory control to food might explain cue elicited overeating in obesity.
Introduction
In Western societies, palatable calorically dense food is omnipresent and relatively cheap compared to healthier foods (Drewnowski & Darmon, 2005). Whereas people used to struggle to obtain enough calories and nutrients, currently a substantial part of the population is struggling to restrict their intake, specifically of energy dense foods. In combating appetite, people need to make an appeal to their self-control (Lowe, 2003). This makes people with less effective self-control vulnerable for overeating and unhealthy weight gain. Research indeed shows that obese people have less effective inhibitory control, compared to those who are lean (Nederkoorn, Havermans, Roefs, Smulders, & Jansen, 2006). Moreover; inhibitory control predicts increased food intake: people with less effective response inhibition eat more during a taste test with palatable, energy dense foods than do people with effective response inhibition (Guerrieri et al., 2007). Not only in adults, but also overweight/obese children and adolescents score lower on tasks measuring inhibitory control and executive functioning (Batterink et al., 2010, Cserjési et al., 2007, Nederkoorn et al., 2006, Verbeken et al., 2009, Verdejo-García et al., 2010). Self-regulatory skills in toddlers 2 years of age even predicted overweight and obesity at 5.5 years of age (Graziano, Calkins, & Keane, 2010).
It seems conceivable that the same lack of inhibitory control would make children vulnerable to other appetitive, rewarding behaviour. Indeed, response inhibition predicts a variety of consumptive behaviours in children and adolescents, including alcohol and tobacco use (Nigg et al., 2006, Riggs et al., 2011). Strangely, the correlation between obesity and other addictive behaviours is often low (Riggs et al., 2011), absent or even negative (Kleiner et al., 2004, Mather et al., 2008). Although ineffective inhibitory control underlies different types of excessive consumption, people who are obese specifically fail in resisting responses towards food and not so much towards other stimuli. Possibly, they acquired conditioned responses to food cues, which are in turn associated with increased food intake. When people are confronted with stimuli that predict food intake, they show cephalic phase responses, including increases in salivation and gastric activity (Nederkoorn et al., 2000, Power and Schulkin, 2008). These responses allow for larger subsequent intake (Mattes, 1997).
Although individuals who are within the normal-weight range exhibit such conditioned food responses (e.g., Cornell, Rodin, & Weingarten, 1989), it appears that obesity in particular is associated with increased appetitive responding to food cues. For example, individuals who are obese show increased salivary response and craving after exposure to food cues, compared to those who are lean (Ferriday and Brunstrom, 2011, Wooley et al., 1975). Similarly, children who are obese tend to eat somewhat more after exposure to food cues than do those who are of healthy weight (Jansen et al., 2003). The increased responsivity of those who are obese also extends to attention to food-related cues, with children who are obese demonstrating more alertness to food adverts than the lean children (Halford, Gillespie, Brown, Pontin, & Dovey, 2004), and adults who are obese showing increased attention for food cues relative to lean participants (Castellanos et al., 2009, Werthmann et al., 2011).
An analogous responsiveness is found in drug users when exposed to relevant drug cues (Carter and Tiffany, 1999, Goldstein and Volkow, 2002). Goldstein and Volkow (2002) suggest in their model that craving or anticipation of substance use leads to a ‘state’ of decreased inhibitory control. Thus, exposure to relevant cues might not only induce cephalic phase responses, but also lessen inhibitory control. It seems therefore plausible that people who are obese are worse at inhibiting responses towards palatable food cues, compared to non-food cues. To our knowledge, this has not been tested yet; it has only been shown that people who are obese have less capacity to inhibit responses towards neutral stimuli than do individuals who are lean. The responsivity to food-related cues appears to follow the same pattern in both adults and children. The current study focused on children because overweight children have an increased risk of being obese as adults (Dietz, 1995), suggesting that the development of early interventions, and increased insight into children’s food-related cue reactivity, are a priority for public health. Inhibition towards food and toy pictures, both with positive valence, was tested. It was hypothesized that a higher BMI would be related to less inhibitory control, especially towards food. In addition, it was expected that the effects would be more pronounced when dividing the children in clinically relevant weight groups.
Section snippets
Participants
Children were recruited from two elementary schools. All parents of children in grades 4 and 5 were sent an information letter, and children who returned a consent form signed by a parent were asked to participate. A total of 91 children were tested, aged 7–9. Two children were excluded because of technical problems. Data were checked for outliers, but all dependent measures were within 3 SD from the mean.
Percentage overweight was calculated by dividing BMI (measured at the end of the
Results
When overweight was entered as a continuous measure, there appeared no influence of hunger or gender on overall inhibition, as measured with SSRT (hunger: F(1, 85) = 0.89, p = 0.35, ηp2 = 0.01; gender: F(1, 85) = 1.1, p = 0.3, ηp2 = 0.01). Overweight had a significant effect on overall inhibition (F(1, 85) = 4.3, p = 0.041, ηp2 = 0.05): children with a higher percentage of overweight performed less well on the stop signal task. When looking at the difference between the food and toy condition, it appeared that
Discussion
It was hypothesized that overweight in children would be related to inhibitory control. In addition, it was hypothesized that children with more overweight would have more difficulties in inhibiting responses towards food stimuli then towards toy stimuli. As expected, we found that in our sample of 7–9 year old children, overweight was related to overall more difficulties with response inhibition. This is in line with previous findings (e.g., Nederkoorn et al., 2006, Verbeken et al., 2009). The
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